The present invention is directed, in general, to the polishing of semiconductor wafers and, more specifically, to a polishing head for delivering slurry, a polishing system employing the polishing head and a method manufacturing an integrated circuit incorporating the polishing head or the polishing system.
In the fabrication of semiconductor components, the various devices are formed in layers upon an underlying substrate, such as silicon. In such semiconductor components, it is desirable that all layers, including insulating layers, have a smooth surface topography, since it is difficult to lithographically image and pattern layers applied to rough surfaces. Conventional chemical/mechanical polishing (CMP) has been developed for providing smooth semiconductor topographies. Typically, a given semiconductor wafer may be polished several times, such as upon completion of each metal layer.
The CMP process involves holding, and optionally rotating, a thin, reasonably flat, semiconductor wafer, held in a carrier head having a retainer ring, against a rotating polishing pad. The wafer may be repositioned radially within a set range as the polishing pad is rotated across the surface of the wafer. The polishing surface, which conventionally includes a polyurethane material affixed to a platen, is wetted by a chemical slurry, under controlled chemical, solid contents, pressure, and temperature conditions. The chemical slurry contains selected chemicals that etch or oxidize selected surfaces of the wafer during the CMP process in preparation for their removal.
Additionally, the slurry contains a polishing agent, such as alumina or silica, that is used as the abrasive material for the mechanical removal of the semiconductor material. The combination of chemical and mechanical removal of material during the polishing process results in superior planarization of the polished surface of the semiconductor wafer. In this process it is important to remove a sufficient amount of material to provide a smooth surface, without removing an excessive amount of underlying materials. To this end, proper slurry distribution during the polishing process is imperative. Accurate material removal is particularly important in today""s submicron technologies where the layers between device and metal levels are constantly getting thinner.
In addition to proper slurry distribution during planarizing, some CMP systems are also directed to controlling the profile of polishing pads so as to control the xe2x80x9cedge effectxe2x80x9d of wafers being polished. Edge effect includes the non-uniform material removal from the edge, versus the center, of semiconductor wafers caused by a flexing in the CMP polishing pad near the wafer edge. As edge effect becomes more predominant, edge exclusion, which is the inability to print and fabricate dies along the edge of the wafer, typically increases. To combat this edge effect, conventional CMP systems attempt to press the retainer ring surrounding the wafer down into the polishing pad. By pressing the retainer ring into the polishing pad, pad deformation occurs under the retainer ring rather than under the edge of the wafer. As a result, edge effect of a semiconductor wafer may be significantly reduced or even eliminated.
Unfortunately, although substantially addressing the problem of edge effect, the prior art techniques introduce other problems. Specifically, to press the retainer ring down into the polishing pad, complex and costly pneumatic or hydraulic systems must be constructed to properly maneuver the retainer ring without damaging the wafer or the polishing pad. In addition, pressing the retainer ring against an abrasive polishing pad eventually wears the ring to the point of needing replacement. Moreover, since the retainer ring surrounds the outer edge of the wafer, pressing the ring into the polishing pad may significantly prevent the distribution of slurry to the wafer surface.
Accordingly, what is needed in the art is a apparatus and method for delivering slurry during a polishing operation that does not suffer from the deficiencies found in the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides a polishing head, for use with a polishing apparatus. In one embodiment, the polishing head includes a carrier head assembly, and a retaining ring having a surface positionable adjacent a polishing pad and couplable to the carrier head assembly and configured to retain a semiconductor wafer therein, the retaining ring having a slurry conduit located therethrough to provide a flow of slurry to the polishing pad.
In another aspect, the present invention provides a polishing system. In one embodiment, the polishing system includes a retaining ring having a surface positionable adjacent a polishing pad and couplable to a carrier head assembly and configured to retain a semiconductor wafer therein, the retaining ring having a slurry conduit formed therein to provide a flow of slurry to the polishing pad. In addition, the polishing system includes a pump configured to deliver the flow of slurry under pressure through the slurry conduit to a surface of the polishing pad.
In yet another aspect, the present invention provides a method of manufacturing an integrated circuit. In an exemplary embodiment, the method includes forming an integrated circuit layer over a semiconductor wafer, and polishing the integrated circuit layer. During the polishing, the method includes flowing a pressurized slurry through a slurry conduit located within a retaining ring of a carrier head assembly and against a surface of a polishing pad, the pressurized slurry causing a surface of the polishing pad located under the retaining ring to deform in a direction away from said retaining ring.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.